It’s back to Ken Rosenberg and his own brand of paranoia. Ken tells you to go and see Ken Paul at the Malibu Club who may have a lead on the missing drugs.
Don’t worry about the inability to purchase the club, as this will all become clear much later in the game when you’ve unlocked it through many more missions.
Ken Paul tells you to go and find a chef on Ocean Drive who may have a lead. The chef will attack you, so either take him out with whatever weapons you’ve acquired or get back into your vehicle and run him over and then pick up his phone which you’ll need for future missions.
Three more chefs will attack you and you can either take them out or just follow Lance into his car. If you pick up a wanted star and want to get rid of it, there’s a star icon to your north down the alley which you just need to walk into.
Lance will show you Ammunation to pick up some weaponry and then you simply drive back to the hotel to complete the mission.